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This forum has attempted to gather Rotax 670 information for years but there has been very little feedback from what I have seen.

I fly a Kitfox and many others who have Avids would consider replacing our 582's with 670's if there was more feed back to back up Rotax Rick's claims.

I purchased the exhaust from Rotax Rick 2 years ago that was to fit inside the cowl of a Kitfox with a 670 and it would not come close to fitting when I mocked it up with my 582 which is virtually the same size as a 670.

That exhaust ended up in Alaska and the new owner thought at first it would fit without modifications in his Kitfox and then months later told me it would not fit.

Currently there is a Kitfox for sale in Florida on Barnstormers for 15K that has a newly installed 670 with 17 hours.

I called the owner just to ask how the 670 install went and he told me the exhaust did not fit as promised and he had to modify it.

He sent photos and the muffler is installed right to left like a 582 kitfox exhaust.

The photos that Rick sent me of a flying Kitfox which had the exhaust he promised to send me had the muffler oriented front to rear.

I would be possibly be flying a 670 today if the exhaust would have been as promised.

I know this is a long and round about way to answer your question.

I assume the Avid 670 install would be upside down as it is with the 582 so the exhaust would not be the same as the Kitfox install.

Rotax Rick is a very friendly and helpful and loaned me the puller to install my RK 400 clutch.

I feel he knows his Rotax engines but something is missing when it comes to the exhaust fitting on the few cases I know of.

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I had a 670 in my Avid MKIV when I originally bought it. The expansion chamber had been cut, turned and brazed in several placed and it fit inside the cowl (inverted engine) but the muffler was outside the cowl, hung under the plane. The original ownner had tried the 582 pipe and said the engine didn't run worth a hoot. If you are good at welding or brazing, maybe just plan on having to build your own from a snow machine pipe.

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Wonder how your coolant temps will be with no cowl lip and the muffler disrupting the airstream at that point. Please keep posting on your experiences with this engine setup. Quite a few of us are interested in how the 670 works out. Jim Chuk

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I have a 670 installed on my KF 4. Mounting the muffler was the most difficult part of the installation. It required cutting and re-welding the "arm" to get it to fit in the cowling. it also required some mounting brackets.

The work was definitely worth it. The 670 has 70+ hours on it now and is running great. The performance increase over the 582 is remarkable. Flying in CO from a field that is 5288 above sea level in the summer with the 582 is a bit lacking, especially with two guys. With the 670 the climb and speed increase is much much much better.

The picture below is not my plane but is the reference for how my exhaust is installed. Works very nicely.

You're going to love the 670 once you get the jetting and prop pitch set correctly. Rick is always pushing to run these engines over rich. That's the only thing I disagree with him on. I have my 670 tuned to be right on at field elevation but remember as we climb up, the mixture will be more rich. Just tune it like a 582 with the next size jet up. I ended up with that and the plug color is a nice light chocolate color, with minimal carbon buildup. The RAVE valves that everyone complains about is not a problem with Rick's engines. He uses the HO spades and they hardly move anyways with the power band we are running the 670 in. Prop it for 6350 ground static. On take off you'll hit 6500 and that's almost perfect.

one last thing, ONLY RUN AMSOIL INTERCEPTOR! it's not that expensive especially if you find an independant amsoil dealer. The cost is 40% less than their stated retail price.

My buddy became a dealer and re-sells to the 6 guys on the field. He makes enough to cover the dealer fee and we all get awesome oil for a reasonable price.

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I never ever promised to any of my customers that my custom 618/ 670 exhaust would fit in a Kitfox without some mod to either the exhaust or cowlings.

There is 6 different Kitfox models & guess what, the exhaust needed for each model is different. I sell 4 different styles of 670 exhaust systems.

A side mount, Rear mount, ( Gyro ) a straight & a Kitfox. Every 618 that was installed in a Kitfox had a re welded exhaust. Rotax never made a Rear mount style exhaust for the 618 . Only a side mount exhaust. Were working right now on modifying the customers 582 exhaust with hopes to see 82 + HP.

I'm sorry if some misunderstood but I never promised a exhaust that would not require some changes.

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"CAUTION " A rich mixture is safe !!!!! You can not trust a EGT gauge in a RAVE Valve engine. The only jetting change from a 582 to a 670 is a 15K2 needle set on the second clip from the top & a 180 Main jet. As for plug colors Chocolate Brown is NOT LIGHT TAN. That's far to lean. Remember the oil is in with the gas .

Never think you can run a 670 below a 175 main jet. Rarely on the low end some engines ( 5% ) need the 15E5U needle that leans the low end.

I want to add one more thing. Rotax makes 3 different angle Y pipes . ( Manifolds ) Straight, slight angled & a steep angle that has s a cut flange to slide over 1 bolt in each cylinder. That gives you several options on installing your exhaust. Keep in mind the 583, 617, 618, 643 & 670 all have interchangeable Y pipes.